1. Field of the Invention
The present invention is broadly concerned with improved feed or food products, (e.g., solid feed supplement blocks or flowable top dressings) which can be fed to animals or humans in order to induce a significant increase in eicosapentaenoic acid (EPA) in the blood plasma of the animals or humans. The invention also is directed to corresponding methods of feeding and to processes for preparing the improved feed or food products.
2. Description of the Prior Art
Much interest has focused on dietary fat and its effect in modulating mammalian immune and inflammatory responses during infection or disease. Dietary lipids affect the immune system in several disease models of rodents and humans. Because dietary fat can alter cell membrane composition, it is a major modulator of immune function (Grimble, 1994; Miles and Calder, 1998). Possible mechanisms include impacting the amount and type of lipid-derived inflammatory mediators (eicosanoids) and inhibiting over-production of certain cytokines produced by cells of the immune system (Calder, 1996).
Eicosanoids are a family of oxygenated derivatives of polyunsaturated fatty acids (PUFA). Two of the omega-6 (n-6) PUFA [arachidonic acid (AA) and dihomo-gamma-linolenic acids] and one omega-3 (n-3) PUFA [eicosapentaenoic acid (EPA)] act as precursors for eicosanoids. These PUFA, as part of the cellular membrane phospholipid, can influence synthesis of eicosanoids such as prostaglandins (PG) and leukotrienes (LT), and platelet activating factor (Miles and Calder, 1998; Calder, 1997; Grimble 1994). Linoleic acid, an n-6 PUFA, is converted to AA in animal cells. In contrast, linolenic acid, an n-3 PUFA, is converted to EPA in animal cells. Whereas AA is a precursor compound to the 2-series PG and the 4-series LT, EPA is a precursor to the 3 and 5-series PG and LT, respectively (Calder, 1997; Grimble 1998). The 2-series PG and 4-series LT are more pro-inflammatory than the 3-series PG and 5-series LT (Calder, 1997; Grimble 1994).
Mulrooney and Grimble (1993) found that feeding butter, fish, and coconut oils, all of which contain low levels of n-6 PUFA, reduced the anorexic effect caused by an intraperitoneal injection of rats with TNF-alpha. In contrast, hepatic and lung protein synthesis, anorexia, and body weight loss were amplified in response to endotoxin injection when dietary n-6 PUFA intake was increased by feeding corn oil compared to feeding butter or olive oil (Besler and Grimble, 1995).
In accordance with these findings, Mascioli et al. (1988; 1989) found that administering guinea pigs fish oil (rich in n-3 PUFA) significantly improved survival after endotoxin infusion compared to animals fed safflower oil. In addition, Pomposelli et al. (1989) observed a reduced interleukin-1 febrile response in guinea pigs fed fish oil compared to those fed safflower oil. These authors conclude that dietary fat can potentially have profound effects on the host animal's response to toxic insults that result in injury and(or) infection.
Cytokines are soluble protein mediators produced by immune cells following activation with stimuli such as infectious diseases. Cytokines play an important role in modulating activity of the immune system and in increasing lipolysis, gluconeogenesis, and muscle proteolysis. The result is provision of substrates for use by the immune system and for acute-phase protein synthesis (Grimble, 1990). While actions of cytokines can be beneficial, excessive or inappropriate production can lead to tissue damage, which occurs in a number of inflammatory diseases (Elsasser et al., 1995). Cytokine production by immune cells is regulated by eicosanoids; since dietary lipids affect eicosanoid production, they also impact cytokine production (Calder, 1998b).
Diets which promote the in vivo synthesis of EPA are known to ameliorate harmful effects of an over-exaggerated, disproportionate inflammatory and immune responses. Accordingly, there is a need in the art for improved animal feeds or human foods which contain fatty acids such as ALA in a form that will enhance and amplify conversion to EPA.